• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.451-457
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• 2007

Four parallel $A^2/O$ systems maintaining an MLSS of 3,000 mg/L were operated to investigate the effects of varying an HRT of anoxic reactors and packing Bio contact media (BCM, fixed beds) in aerobic reactors on organic matter removal and nitrification/denitrification efficiencies. All systems were operated under conditions that the external recycle ratio was kept 0.5 Q while the internal recycle ratio was changed 1.0 Q to 1.5 Q with that $NH_4-N$ concentration of feed was increased to 40 mg/L by adding $NH_4Cl$. In terms of TSS and TCODcr removal efficiency, both systems with BCM and a system without BCM, respectively, had a similar level of the removal efficiency under varied HRTs of anoxic reactors (0.6 hr, 1.3 hr, 2 hr, 2 hr; control, without BC M) showing that varying an HRT of anoxic reactors did not affect the removal efficiency. While SCODcr removal efficiency of systems with BCM was improved approximately 4~5% at the same HRT of anoxic reactor, the removal efficiency of system with BCM was slightly decreased by reducing an HRT of anoxic reactor. The nitrification efficiency for both systems with BCM and a system without BCM was above 94% showing that packing BCM in aerobic reactors and varying an HRT of anoxic reactors did not affect the efficiency significantly despite of increasing $NH_4-N$ concentration of feed. The denitrification efficiency increased from 81.4% to 85.4% at system with BCM while the efficiency decreased when a shorter HRT of anoxic reactors was kept. The excellent effluent quality for $NO_3-N$ concentration was observed although the $NO_3-N$ concentration increased in anoxic reactors that $NH_4-N$ concentration of feed sufficiently converted into nitrate through nitrification. As a result, packing 20% BCM to an aerobic reactor with HRT of 1.3 hr of anoxic reactor in $A^2/O$ system can achieve a similar level of nitrogen removal efficiency in $A^2/O$ system which the aerobic reactor had no BCM and HRT of 2 hr for anoxic reactor is maintained.

• Journal of Korean Society on Water Environment
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• v.24 no.6
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• pp.659-669
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• 2008

Two sets of four parallel activated sludge reactors (ASRs) maintaining an MLSS of 3000 mg/L were operated to investigate the effect of DO, HRTs and bio-contact media (BCM) packing ratios on the removal efficiency of organic matters and nitrogen. Packing ratios of BCM to BCM-ASR systems 1, 2, 3, and 4 were 0% (suspended growth only), 10%, 15% and 20%, respectively. All systems were operated at an HRT of 4 hr, 6 hr, and 8 hr, respectively; DO concentration was maintained 0.5~1.0 mg/L and 1.5~2.0 mg/L for each HRT condition. In terms of TSS, TCODcr and SCODcr removal efficiency, all systems had a similar level of the removal efficiency under varied HRTs, and DO. But organic removal efficiency of systems with BCM was approximately 3~5% higher than systems without BCM at the same HRT and the DO. About the nitrification efficiency, with high DO (1.5~2.0 mg/L), as HRT (4 hr, 6 hr, 8 hr) or BCM packing ratio increased, the slight increment of nitrification efficiency was observed. However, under the low DO (0.5~1.0 mg/L), increase of BCM packing ratio and HRT resulted in large increase of the nitrification efficiency. At the same HRT and BCM packing ratio, the nitrification efficiency increased greatly with up to 15% as DO increased. When the HRT increased from 4hr to 8hr, the denitrification efficiency slightly increased by 5~10% only, under all DO conditions. Systems with BCM had higher denitrification efficiency, ranged 62.7~91.1% than systems without BCM showed 32.1~65.6%. And the increase in BCM packing ratio from 10% to 20% resulted in about 14~16% denitrification efficiency increment. BCM packing ratio showed great effect on the denitrification. The increase of the DO (from 0.5~1.0 mg/L to 1.5~2.0 mg/L) at the same HRT and BCM packing ratio resulted in slight decrease of denitrification efficiency with up to 7% for systems with BCM. But for systems without BCM, the denitrification efficiency decreased with up to 28%. In all system, the denitrification efficiency had more influence on the TN removal efficiency than nitrification efficiency. So, BCM packing ratio (0%, 10%, 15%, 20%) has greater effect on the TN removal than HRT and DO. The TN removal efficiency increased as packing ratio of BCM increased with up to 45%. As a result, the highest TN removal efficiency was observed 73.7% at the condition showed the highest denitrification efficiency that DO of 0.5~1.0 mg/L, an HRT of 8 hr, and 20% of BCM packing ratio was maintained.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.1022-1030
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• 2006

Activated sludge reactors maintaining an MLSS of 3,000 mg/L and packed Bio Contact Media (BCM fixed beds) was studied in lab-scale to determine the optimal packing ratio and an HRT of aerobic reactor in terms of organic removal, nitrification, denitrification efficiencies. At all HRTs of 3 hr, 5 hr, 7 hr respectively, reactors without BCM, control reactors, had the lowest TCODcr removal efficiency about 74.6%, and reactors with the BCM packing ratios of 10%, 15%, 20% had a greater TCODcr removal efficiency above 81.4%. As HRT decreased, the TCODcr removal efficiency decreased also in all reactors. However, a better utilization of TCODcr even at a higher organic loading was observed in reactors with BCM. The nitrification efficiency at all reactors was greater than 94%, and reactor with 20% packing of BCM had the highest nitrification efficiency at 97.9% while the TKN loading increased at $0.085mgTKN/m^3{\ast}day$ as HRT decreased, In terms of denitrification efficiency, the reactor without BCM ranged from 11.6% to 13.7%, and the reactors with BCM ranged from 28.3% to 63.4% which suggests that the more BCM is packed in the reactors, the higher the denitrification efficiency is achieved. Two parallel $A^2/O$ systems maintaining an MLSS of 3,000 mg/L were operated to investigate the effect of BCM packing ratio of 20% on organic removal, nitrification, denitrification efficiencies. Packing with BCM in system of aerobic reactor affected the SCODcr removal efficiency that increased from 73% to 78%. The nitrification efficiency for both systems with or without BCM was greater than 95%. The denitrification efficiency of systems with BCM and without BCM was 85.8% and 81.8%, respectively which appears that the denitrification efficiency was increased slightly by packing BCM. Compared denitrification efficiency in $A^2/O$ system to previous experimental study with activated sludge reactors operates with the same HRT $A^2/O$ system showed only 29% greater denitrification efficiency. It suggests that $A^2/O$ system with BCM can achieve a similar level of denitrification efficiency when the HRT of anoxic reactor is decreased to some extent.